Stair step formation using at least two masks

ABSTRACT

Apparatuses and methods for stair step formation using at least two masks, such as in a memory device, are provided. One example method can include forming a first mask over a conductive material to define a first exposed area, and forming a second mask over a portion of the first exposed area to define a second exposed area, the second exposed area is less than the first exposed area. Conductive material is removed from the second exposed area. An initial first dimension of the second mask is less than a first dimension of the first exposed area and an initial second dimension of the second mask is at least a second dimension of the first exposed area plus a distance equal to a difference between the initial first dimension of the second mask and a final first dimension of the second mask after a stair step structure is formed.

PRIORITY INFORMATION

This application is a Continuation of U.S. application Ser. No.14/797,390, filed Jul. 13, 2015, which issues as U.S. Pat. No. 9,508,591on Nov. 29, 2016, which is a Continuation of U.S. application Ser. No.14/085,361, filed Nov. 20, 2013, which issued as U.S. Pat. No. 9,082,772on Jul. 14, 2015, which is a Divisional of U.S. application Ser. No.13/543,154, filed Jul. 6, 2012, which issued as U.S. Pat. No. 8,609,536on Dec. 17, 2013.

TECHNICAL FIELD

The present disclosure relates generally to semiconductor memoryapparatuses and methods of forming, and more particularly, toapparatuses and methods for stair step formation using at least twomasks.

BACKGROUND

Memory devices are typically provided as internal, semiconductor,integrated circuits in computers or other electronic devices. There aremany different types of memory, including random-access memory (RAM),read only memory (ROM), dynamic random access memory (DRAM), synchronousdynamic random access memory (SDRAM), resistive memory, e.g., RRAM, andFlash memory, among others.

Memory devices are utilized as volatile and non-volatile data storagefor a wide range of electronic applications. Flash memory typically usesa one-transistor memory cell that allows for high memory densities, highreliability, and low power consumption. Non-volatile memory may be usedin, for example, personal computers, portable memory sticks, solid statedrives (SSDs), digital cameras, cellular telephones, portable musicplayers such as MP3 players, movie players, and other electronicdevices.

Memory devices can comprise memory arrays of memory cells, which can bearranged in various two or three dimensional configurations. Circuitrycoupled to a memory array can be arranged in a substantially planarconfiguration, for instance. Interconnections are used to couple memorycells and associated circuitry.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a prior art perspective view of a portion of a threedimensional (3D) memory device.

FIG. 2 is a prior art schematic diagram illustrating connections betweena memory array and a string driver.

FIG. 3 is a prior art isolated perspective block diagram illustratingconnections between a 3D memory array and a planar string driver.

FIGS. 4A-4F are prior art block diagrams illustrating a side view ofstair step formation using a shrinking photo resist.

FIGS. 5A-5F are block diagrams illustrating a top view of stair stepformation using a shrinking photo resist in accordance with one or moreembodiments of the present disclosure.

FIGS. 6A-6B are prior art block diagrams illustrating stair stepformation in four directions.

FIG. 7A is a block diagram illustrating stair step formation in twodirections using two masks in accordance with one or more embodiments ofthe present disclosure.

FIG. 7B is a block diagram illustrating stair step formation in onedirection using two masks in accordance with one or more embodiments ofthe present disclosure.

FIGS. 8A-8L are block diagrams illustrating stair step formation in onedirection using two masks in accordance with one or more embodiments ofthe present disclosure.

DETAILED DESCRIPTION

Apparatuses and methods for stair step formation using at least twomasks, such as in a memory device, are provided. One example method caninclude forming a first mask over a conductive material to define afirst exposed area, and forming a second mask over a portion of thefirst exposed area to define a second exposed area, the second exposedarea being less than the first exposed area. Conductive material isremoved from the second exposed area. An initial length of the secondmask is less than a length of the first exposed area and an initialwidth of the second mask is at least a width of the first exposed areaplus a distance equal to a difference between the initial length of thesecond mask and a final length of the second mask after a stair stepstructure is formed.

In the following detailed description of the present disclosure,reference is made to the accompanying drawings that form a part hereof,and in which is shown by way of illustration how one or more embodimentsof the disclosure may be practiced. These embodiments are described insufficient detail to enable those of ordinary skill in the art topractice the embodiments of this disclosure, and it is to be understoodthat other embodiments may be utilized and that process, electrical,and/or structural changes may be made without departing from the scopeof the present disclosure.

The figures herein follow a numbering convention in which the firstdigit or digits correspond to the drawing figure number and theremaining digits identify an element or component in the drawing.Similar elements or components between different figures may beidentified by the use of similar digits. As will be appreciated,elements shown in the various embodiments herein can be added,exchanged, and/or eliminated so as to provide a number of additionalembodiments of the present disclosure. In addition, the proportion andthe relative scale of the elements provided in the figures are intendedto illustrate various embodiments of the present disclosure and are notto be used in a limiting sense.

The terms “first,” “second,” “third,” and “fourth” may be used herein,and/or in the claims, merely for convenience in differentiating thenomenclature of various features from one another. The use of such termsdoes not necessarily imply that the materials are of differentcomposition, but sometimes are used to distinguish between materialsformed at different elevations, at different times, or in differentmanners, even if of the same composition. The use of such terms does notintend to convey a particular ordering of the features, including, butnot limited to, an order of forming.

FIG. 1 is a prior art perspective view of a portion of a threedimensional (3D) memory device 100. The memory device 100 can comprise,for example, a NAND flash memory array. Memory device 100 includes anumber of vertical strings of series-coupled memory cells 103 orientedorthogonal to a number of conductive lines, such as access lines 105and/or data lines 102. As used herein, A “coupled to” B refers to A andB being operatively coupled together, such as where A and B areelectrically connected with each other, such as through a direct ohmicconnection or through an indirect connection, e.g., via C. Insulatingmaterials between various conductive lines are omitted from FIG. 1 forclarity. Conductive materials can be formed of polysilicon, for example,or other doped or undoped materials. Insulating materials can be formedof oxide, for example, or other dielectric materials.

A first select gate 108, such as a drain select gate (SGD), can bearranged at a first end of a number of the vertical strings ofseries-coupled memory cells 103, and a second select gate 110, such as asource select gate (SGS), can be arranged at a second end, e.g.,opposite end, of the vertical strings of series-coupled memory cells103.

A plurality of data lines 102 can be oriented in a first plane, andfurther oriented in a first direction in the first plane, the verticalstrings of series-coupled memory cells 103 being oriented orthogonal tothe first plane. A plurality of access lines 105 can be oriented in asecond plane, and further oriented in a second direction in the secondplane.

As shown in FIG. 1, the access lines 105 can be formed in a planarconfiguration. The second plane can be substantially parallel to thefirst plane. The second direction can be perpendicular to the firstdirection, for example. The data lines 102 can be shared by a number ofvertical strings of series-coupled memory cells 103 in the firstdirection, and the access lines 105 can be shared by a number ofvertical strings of series-coupled memory cells 103 in the seconddirection.

One or more source lines 104 can be oriented in a third plane, the thirdplane being substantially parallel to the first and second planes. Thesource lines 104 can be further oriented in the second direction, e.g.,the same direction as the access lines 105 as shown in FIG. 1, or adifferent direction. The select gates 108 and 110 can operate to selecta particular vertical string of series-coupled memory cells 103 betweena data line 102 and a source line 104. As such, the vertical strings ofseries-coupled memory devices 103 can be located at the intersections ofthe data lines 102 and source line 104.

The access lines 105 are coupled to (and in some cases from) controlgates of memory cells at a particular level and can be used to select aparticular one of the series-coupled memory cells within a verticalstring. In this manner, a particular memory cell can be selected andelectrically coupled to a data line 102 via operation of the firstselect gate 108, second select gate 110, and an access line 105. Theaccess lines 105 can be configured to select a memory cell at aparticular location within one or more of the vertical strings ofseries-coupled memory cells 103.

As can be observed in FIG. 1, the planar access lines 105 can beconfigured to have multiple 3D stair step structures 106 to facilitatevertically-oriented coupling thereto, such as by vertical conductors112. That is, respective planar access lines 105 can be formed asrespective stair steps of the stair step structure 106. A stair stepstructure 106, as used herein, means a 3D structure having a pluralityof stair steps at different elevations extending to different distancesin a lateral direction, such as is generally associated with a set ofstair steps. According to one embodiment of the present disclosure, thesteps of lower elevations can extend laterally beyond the lateraldistance that the step at an immediately higher elevation extends, asshown in FIG. 1. That is, lower steps extend further in a lateraldirection than step(s) above. FIG. 1 shows steps on two ends of theplanar access lines 105, but not on the nearest edge. According to aprevious approach, steps are formed on all edges and subsequentlytrimmed away from those edges at which steps were not wanted therebywasting the area where steps were formed and subsequently removed. Suchwasted area can increases the effective footprint of the memory device100.

For example, FIG. 1 shows a stack of materials comprising at least thefirst select gate 108, access lines 105, second select gate 110, havingthree of four edges formed to have a stair step configuration. AlthoughFIG. 1 shows a stack of materials having edges formed into a stair stepconfiguration, it is not prior art to only form a portion of an edge ofthe stack of materials into a stair step configuration, as discussedlater. Embodiments of the present disclosure can include a stack ofmaterials having one or more edges having a stair step configuration.Embodiments of the present disclosure can include only a portion, e.g.,less than all, of an edge of a stack formed into a stair stepconfiguration. For example, embodiments of the present disclosure caninclude that a first portion of one edge of a stack of materials can beformed to have a stair step configuration and a second portion of theone edge can be formed so as not to have a stair step configuration, aswill be detailed further herein.

A lower step can extend laterally a sufficient distance beyond a nexthigher step so that a vertical coupling can be made to the portion ofthe lower step extending laterally past the next higher step. In thismanner, a vertical conductor 112 can be coupled to the lower step, suchas to an access line 105, select gate 108 or 110, or source line 104,which each can correspond to a step in the stair step structure 106.

The memory array 100 can be coupled to various circuitry associated withoperating the memory array 100. Such circuitry can include string drivercircuitry, for instance. As an example, horizontal conductive lines 114can be routed from the memory array 100, for example, to a stringdriver. Steps of the stair step structure 106 can be coupled to theconductive lines 114, e.g., via the vertical conductors 112. In thismanner, an electrical coupling can be made between the vertical stack ofaccess lines 105, select gates 108/110, and/or source lines 104, and thestring driver, e.g., via the planar horizontal conductive lines 114.

The strings of NAND memory cells can be arranged with select gatetransistors coupled at each end, e.g., source, drain. Each string caninclude a number of memory cells coupled in series, drain-to-source.Vertical strings of NAND memory cells can be arranged such that thestring of series-coupled memory cells are linearly arranged in avertical orientation, or can be arranged in non-linear configurationsuch as in a “U” shape, with portions of the “U” shape being orientedvertically, for example. That is, the string of series-coupled memorycells can be arranged in a dimension orthogonal to the planesencompassing the access lines, e.g., word lines, and data lines, e.g.,bit lines.

FIG. 2 is a prior art schematic diagram illustrating coupling between amemory array 200 and a string driver 216. String driver 216 can be usedto control selection of particular strings of memory cells and/orparticular memory cells, such as by application of a voltage signal ofparticular select gates and/or particular memory cells within thestrings of memory cells, e.g., by appropriate assertion of access lines206. FIG. 2 shows the access lines 206, select gate 208 (SGD), andselect gate 210 (SGS) of a memory array 200 being coupled to a stringdriver 216 via a number of conductive lines 214. The string driver 216can be formed using CMOS devices, for example. The memory array 200further includes the data lines 202 arranged as shown and coupled to thestrings of memory cells.

The access lines 206, select gate 208 (SGD), and select gate 210 (SGS)of a memory array 200 can be coupled to respective global access lines228 through selection transistors 218. The selection transistors 218 canbe field effect transistors (FETs), for example. The selectiontransistors 218 can be controlled via the block high voltage switchoutput (BLKHVSW_OUT) signal line 226, which is coupled between an outputof a block high voltage switch 220 and, for example, the gate of each ofthe selection transistors 218. The block high voltage switch 220receives as inputs, for example, a block selection address 222 and aninput voltage 224 to produce the BLKHVSW_OUT signal on the block highvoltage switch output signal line 226 when appropriate to couple theaccess lines 206, select gate 208 (SGD), and select gate 210 (SGS) ofmemory array 200 to the global access lines 228.

In a sensing operation, such as a read or a program verify operation,global access line driver 216 provides positive voltage signals toglobal access lines 228, e.g., global word lines, to select a particularlocal access line coupled to memory cells being sensed. Unselectedaccess lines, such as access lines not coupled to memory cells beingread or verified, can be provided with a pass voltage (Vpass), while theselected access line can be provided with a read voltage. Othertechniques are possible for reading and/or programming memory cells.According to various embodiments, the memory array 200 can beimplemented as a 3D memory array with the strings being orientedvertically and the string driver 216, including the selectiontransistors 218, can be implemented as a substantially planar device,such as is shown in FIG. 3. A stair step structure comprising theconductive lines 214 can be used to electrically couple the vertical 3Darray and horizontal planar structures, e.g., string driver 216.

FIG. 3 is a prior art isolated perspective block diagram illustratingcoupling between a 3D memory array and a planar string driver. FIG. 3shows, in isolation, the use of a stair step structure to couple avertical stack structure, e.g., a 3D memory array and a substantiallyplanar structure, e.g., planar string driver 316. The vertical stackstructure is comprised of a number of steps of conductive materialsincluding a select gate 308, e.g., SGD, a plurality of access lines 306,e.g., 8 steps of word lines, and a select gate 310, e.g., SGS, of amemory array. Vertical strings of series-coupled memory cells 303 arearranged orthogonally to the steps of the vertical stack structure (onlytwo of many vertical strings are shown in FIG. 3 for simplicity).

Vertical conductors 312 are shown coupled to the various steps where alower step extends beyond the step above the respective lower step. Thevertical conductors 312 are coupled to horizontal conductive lines 314,which in turn are coupled to the substantially planar string driver 316,such as in the manner shown schematically in FIG. 2. The conductors,transistors, and/or other elements of the string driver 316 are threedimensional, and thus not strictly planar, in that they have a finitelength, width, and height. However, the string driver is referred toherein as being substantially planar in that the dimensions in twodirections are significantly greater than the dimension in the thirddirection. For example, planar can refer to a structure havingnon-stacked elements, whereas 3D can refer to a structure that hasstacked elements, e.g., a plurality of elements in each of threedimensions.

FIGS. 4A-4F are prior art block diagrams illustrating a side view ofstair step formation using a shrinking photo resist. FIG. 4A shows astack 409 of alternating conductive materials and insulating materials407-1, 407-2, . . . 407-5. The conductive materials can include a selectgate 408 material, e.g., a drain select gate material, formed over aplurality of access line 406-0, 406-1, 406-2, and 406-3 materials,formed over a select gate 410 material, e.g., a source select gatematerial. Although only materials of four access lines 406-0, 406-1,406-2, and 406-3 are shown in stack 409, embodiments of the presentdisclosure are not limited to a stack comprising a particular quantity,order, or composition of materials, and may include more or fewer accessline materials, select gate materials, and/or other materials.Furthermore, the stack 409 need not be formed by alternating singleconductive and insulating materials, and can include, for example,several conductive materials separated by two different insulatingmaterials formed adjacent one another (which can be considered asconductive and insulating materials), as well as other combinations andconfigurations of materials.

A photo resist 430-1 is formed over the stack 409. As shown in FIG. 4A,the photo resist 430-1 can be formed such that it does not extendlaterally to edges of the stack 409. That is, the photo resist 430-1 canbe formed to be smaller in each dimension than the stack 409, so as toleave a lateral portion of the stack 409 exposed in each direction.Although the side view of cut through the stack of materials of FIG. 4Ashows the photo resist not extending to two opposite edges of the stack409, e.g., right and left, the prior art photo resist 430-1 is formed soas to not extend to the edges in the direction of the view, e.g., frontand back edges, of stack 409. The photo resist 430-1 is formed so as toleave the width of one stair step of stack 430-1 exposed at each edge ofthe stack 409.

FIG. 4B shows the configuration of stack 409 after a first materialremoval process, e.g., an etch of polysilicon materials and oxidematerials such as a reactive ion etch. Portions of stack 409 notprotected by photo resist 430-1 are removed. The material removalprocess is controlled so as to remove material of the stack 409 to apredefined depth, such as by duration and/or composition of the etch, orby other technique. For example, FIG. 4B shows that the first materialremoval process removed material from stack 409 to a depth of insulatingmaterial 407-4, including portions of select gate 408 material,insulating material 407-5, and access line 406-3 material not covered byphoto resist 430-1. The first removal process can be stopped at thedepth of the access line 406-3 material, e.g., removing only the selectgate 408 material and insulating material 407-5, so as to form a firststair step that does not include the access line 406-3 material.

In this manner a stair step is formed of the select gate 408 material,insulating material 407-5, and access line 406-3 material, with respectto the rest of the materials of stack 409. FIG. 4B shows the stair stepbeing formed at two opposite edges of stack 409 simultaneously.Likewise, steps are formed at the front and back edges.

FIG. 4C shows the photo resist 430-2 being re-sized in a lateraldimension from that of photo resist 430-1 shown in FIGS. 4A and 4B so asto expose another portion of the top material of the stack 409, e.g.,select gate 408 material. The photo resist is also resized to be smallerin the direction of the view of FIG. 4C, e.g., front-to-back. Re-sizingof the photo resist 430-2 can be accomplished by various techniques. Forexample, the photo resist 430-1 shown in FIGS. 4A and 4B can be trimmedin place, or removed completely such as by chemical mechanical polishing(CMP) and a new photo resist 430-2 of smaller dimensions deposited overselect gate 408 material as shown in FIG. 4C. The photo resist 430-1 canbe trimmed in place, for example, during polysilicon and oxide dryetching used to create respective stair steps, e.g., such that anintervening structure such as that shown in FIG. 4B would not exist.

FIG. 4D shows the configuration of stack 409 after a subsequent materialremoval process, e.g., a second etch. Some depth of material of stack409 not protected by photo resist 430-2 is removed. The material removalprocess is controlled so as to remove material of the stack 409 to apredefined depth. For example, FIG. 4D shows that the second materialremoval process is controlled to remove material from stack 409including another portion of exposed select gate 408 material,insulating material 407-5, and access line 406-3 material not covered byphoto resist 430-2. The second material removal process also removesinsulating material 407-4 (exposed by the first material removalprocess) and access line 406-2 material, which is exposed afterinsulating material 407-4 is removed during the second material removalprocess. FIG. 4D shows a stair step structure with the two (right andleft) steps resulting from the second removal process. Similarly,additional steps are simultaneously formed on front and back edges ofthe stack according to the previous approach. Note that the nomenclatureused herein is based on a step is a “notch” cut into the stack ofmaterials, the notch being a corner formed by a horizontal surface and avertical surface. Accordingly, FIG. 4A shows zero steps (instead ofone), FIGS. 4B and 4C show one step (instead of two), and FIG. 4D showstwo steps (instead of three).

The material removal processes can be further repeated, each subsequentremoval process utilizing a photo resist mask that is smaller by a stairstep width associated with each respective location of stair stepformation, e.g., each of left, right, front, and back edges. A stairstep width can be 10 micro meters, for example.

FIG. 4E shows the configuration of stack 409 after four material removalprocesses, e.g., four etches, where photo resist 430-3 is reduced by thewidth of several steps on each edge with respect to photo resist 430-2.FIG. 4F shows the configuration of stack 409 after the four materialremoval processes and after the photo resist 430-3 is removed, e.g., byCMP, leaving a final stair step structure. Although each stair step isshown with a respective insulating material atop the stair step (selectgate material 408 is not counted as a step), vertical coupling can bemade to each respective underlying conductive material, e.g., selectgate material and/or access line material, using further etch techniquesto form a plug through overlying insulating layers.

FIGS. 5A-5F are block diagrams illustrating a top view of stair stepformation using a shrinking photo resist in accordance with one or moreembodiments of the present disclosure. FIGS. 5A-5F are top views thatcorrespond to the side views shown in FIGS. 4A-4F. That is, FIG. 5A is atop view that corresponds to FIG. 4A, FIG. 5B is a top view thatcorresponds to FIG. 4B, etc. As previously detailed, reference numbersalso correspond between FIGS. 5A-5F and 4A-4F, with the first digitreflecting the appropriate figure number.

FIG. 5A shows a photo resist 530-1 formed over a stack of alternatingconductive materials and insulating materials, e.g., stack 409 shown inprofile in FIG. 4A. More particularly, photo resist 530-1 is formed overthe select gate 508 material, which is the top material of the stack. Asshown, the photo resist 530-1 can be formed such that it does not extendlaterally, e.g., left-to-right in FIG. 5A, to one or more edges of theselect gate 508 material. For example, the photo resist 530-1 can beformed to be smaller in at least one dimension than the select gate 508material so as to leave a portion of the select gate 508 materialexposed at the left and right edges.

The top view shown in FIG. 5A shows that the photo resist 530-1 can beformed over the select gate 508 material so as to extend to or past anedge(s) of select gate 508 material at which a stair step structure inthe stack is not to be formed, such as at the upper and lower edges ofthe select gate 508 material shown in FIG. 5A. The photo resist 530-1can extend to or past the upper and lower edges of the select gate 508material, as shown in FIG. 5A. According to one or more embodiments,photo resist 530-1 can be formed to extend past the edges of the selectgate 508 material by a distance equal to the total distance by which thephoto resist is subsequently reduced for all material removal processes.With such an overlap, proportional reduction of the photo resist in eachof the two dimensions shown in FIG. 5A will result in the smallest photoresist still extending to the edges of select gate 508 material at whicha stair step structure in the stack is not to be formed.

FIG. 5B shows the configuration of the stack after a first materialremoval process, e.g., an etch. Some material of the stack not protectedby photo resist 530-1 is removed. The first material removal process iscontrolled so as to remove material of the stack to the depth ofinsulating material 507-4. That is, portions of select gate 508material, as well as underlying insulating material and access linematerial not protected by photo resist 530-1 has been removed.

FIG. 5C shows the photo resist 530-2 being re-sized from that of photoresist 530-1 shown in FIGS. 5A and 5B so as to expose another portion ofselect gate 508 material at the top of the stack of materials. Theinsulating material 507-4, exposed by the first material removalprocess, also remains exposed. Re-sizing of the photo resist 530-2 isshown being of reduced size in not only the lateral dimension, e.g.,left-right, but also reduced by a proportional amount in a perpendiculardimension, e.g., top-bottom. The photo resist can be re-sized in alldimensions during a dry etch of the polysilicon and oxide, for instance.

Therefore, while forming stair steps in one direction, e.g., thehorizontal direction in FIG. 5C, the width of the photo resist, e.g., inthe vertical direction shown in FIG. 5C, can be maintained so as not tobe reduced in width so as to expose the conductive and/or insulatingmaterials underneath at the upper or lower edges. Therefore the width ofthe photo resist can initially be formed to extend beyond an edge of theselect gate material 508. This can mandate the silicon area be larger inthe vertical direction shown in FIG. 5C so that the photo resist can beformed thereover, which can consume a larger volume and footprint.

However, even with the reduction in size of the photo resist 530-2, thephoto resist 530-2 still extends past the edges of the select gate 508material at which stair step formation is not to occur, e.g., at theupper and lower edges of the select gate 508 material. This proportionalover-extension of the photo resist beyond edges of the select gate 508material at which stair step structure is not to be formed can beutilized where the photo resist is re-sized in place, such as bytrimming or etch of the photo resist material.

FIG. 5D shows the configuration of the stack after a second materialremoval process, e.g., a second etch. A depth of material of the stacknot protected by photo resist 530-2 is removed, including anotherportion of exposed select gate material 508, insulating material, andaccess line material not covered by photo resist 530-2 to exposeinsulating material 507-4. The second material removal process alsosimultaneously removes the insulating material 507-4 exposed by thefirst material removal process and access line material beneath theexposed insulating material 507-4 to expose insulating material 507-3 asa second stair step. Therefore, FIG. 5D shows a stair step structurewith two steps resulting from the second removal process, correspondingto the side view shown in FIG. 4D.

As described above, the material removal processes can be furtherrepeated, each one utilizing a photo resist that is smaller by a stairstep width on each respective location of stair step formation, e.g.,each of left and right edges, and optionally, smaller by a similaramount in the perpendicular direction. FIG. 5E shows the configurationof stack after four material removal processes to create additionalsteps, including four steps respectively having insulating layers 507-1,507-2, 507-3, and 507-4 atop the respective steps.

FIG. 5E corresponds to the side view of the stack shown in FIG. 4E,where photo resist 530-3 has been reduced by the width of several stepson each side with respect to photo resist 530-2. FIG. 5E shows thatphoto resist 530-3 has been similarly reduced to the upper and loweredges of insulating material 507-4 by the last re-sizing of the photoresist. FIG. 5F shows the configuration of stair step structure of thestack corresponding to FIG. 4F after the four material removal processesand after the photo resist 530-3 is removed, e.g., by CMP, leaving afinal stair step structure with the select gate 508 material exposed.

FIGS. 6A-6B are prior art block diagrams illustrating stair stepformation at four edges of stack materials. FIG. 6A shows a top view ofa stack of materials configured into a stair step structure at each offour edges of the stack. FIG. 6A shows the stack having a plurality ofstair steps, including a first (bottom) step 634 that extends beyond asecond step 636, which extends beyond a third step 638, which extendsbeyond a fourth step 640, which extends beyond a fifth (top) step 642.Vias 644 can be formed into the stack, and memory cells can be formedtherein (vias shown in outline in FIG. 6B since insulating materials notshown).

The stair step structure shown in FIG. 6A can be formed in a similarmanner to that described with respect to FIGS. 4A-4F using a photoresist that does not extend to (or beyond) any of the four edges, suchthat a stair step structure is formed at each edge. Although only fivesteps are shown in FIG. 6A, the quantity and sizing of the steps is notlimited to those shown, and can include more or fewer steps of the sameor different sizes.

FIG. 6B shows a side view of the conductive materials of the stack shownin FIG. 6A. Insulating materials of the stack, such as may be betweenthe select gate materials and/or access line materials are omitted forclarity.

FIG. 7A is a block diagram illustrating stair step formation at only aportion of each of two edges of a stack of materials using an area maskin accordance with one or more embodiments of the present disclosure.FIG. 7A shows an area mask 750A having an opening 752A, e.g., window,therethrough. The area mask can be a hard mask, for example, formed ofsilicon nitride, silicon oxide, silicon oxynitride, aluminum oxide, orthe like. That is, a hard mask material can be formed over the stack ofconductive and insulating materials and patterned and etched to form theopening 752A.

According to various embodiments, the area mask 750A is formed over thestack of conductive and insulating materials with the openingtherethrough so as to expose an area of the stacked materials, e.g.,conductive material, in which a stair step structure is to be formed. Inthis manner, the area mask 750A can define a first exposed area of thestack of conductive materials, which is left exposed through opening752A.

A photo resist mask can be formed over the opening 752A, extending to,or past, e.g., overlapping, the area mask 750A. According to someembodiments, the photo resist mask can formed of a material that has anetching rate greater than that of the area mask. According to variousembodiments, the photo resist mask can be formed over a portion of thefirst exposed area of the conductive material. In this manner, the photoresist mask can define a second exposed area, the second exposed areabeing less than the first exposed area. For example, the second exposedarea 746 is defined within opening 752A in part by photo resist mask753.

According to various embodiments, the second exposed area is less thanall of the first exposed area of the conductive material. For example,the photo resist mask can be formed first as shown at 753 for a firstmaterial removal process leaving areas 746 of the stack, e.g.,conductive material, exposed and subject to material removal. Conductivematerial (and underlying insulating and/or conductive materials) in area746 do not have portions of the area mask 750A or the photo resist mask,e.g., 753, formed thereover. As can be seen in FIG. 7A, an initialdimension, e.g., length (shown in FIG. 7A in the horizontal, or X,direction), of the photo resist mask 753 can be less than acorresponding dimension, e.g., length, of the first exposed area, asdefined by opening 752A in area mask 750A.

An initial width, e.g., in the vertical Y direction shown in FIG. 7A, ofthe photo resist mask 753 can be at least a width of the area mask plusa distance equal to the difference between the initial length of thephoto resist mask and a final length of the photo resist mask after thestair step structure is formed. That is, the photo resist mask may beetched away and/or trimmed to a smaller size and used to subsequentlyform additional stair steps. The initial width of the photo resist maskcan be at least the width of the area mask plus an overlap distance. Theamount of initial overlap, e.g., overlap distance, can be, for example,equal to a difference in the length of the photo resist mask between theinitial length of the photo resist mask and a final length of the photoresist mask after the stair step structure is formed.

The amount of initial overlap can depend on how many stair stepscomprise the stair step structure. According to some embodiments, theinitial width of the photo resist mask can be at least the width of thearea mask plus a product of a number of stair steps in the stair stepstructure times an amount by which the photo resist mask is resized toform one stair step. That is, if the photo resist mask is etched and/ortrimmed all around a same distance between material removal to formrespective stair steps, then in order to maintain some overlap, or atleast abut an edge of the area mask for the last step formation so asnot to allow unintended removal of material, the photo resist mask canbe oversized with respect to the width of the area mask window by anamount per stair step times the quantity of stair steps.

According to a number of embodiments, the photo resist mask caninitially overlap the portion of the area mask by an amount by which thephoto resist mask is reduced to form a next stair step times a quantityof stair steps to be formed. For instance, a stair step structureinvolving two stair steps can be formed by two material removalprocesses, which typically only involves resizing the photo resist maskonce. Therefore, the photo resist mask can initially overlap the areamask by the distance that the photo resist mask is reduced in sizeduring one material removal process. A stair step structure involvingthree stair steps can be formed by using two photo resist maskresizings, e.g., 3−1=2. Therefore, the photo resist mask can initiallyoverlap the area mask by the distance that the photo resist mask isreduced in size during two photo resist mask resizings.

As shown in FIG. 7A, a stair step structure can be formed involving anarea 746 at the right side of opening 752A and an area 746 at the leftside of opening 752A. The two exposed areas 746 are shown beingnon-contiguous, with the photo resist mask formed between areas 746. Thearea mask 750A can be formed to configure the opening 752A to be anon-square rectangle, as shown in FIG. 7A. However, embodiments of thepresent disclosure are not so limited, and area 746 can be of varioussizes, shapes, and/or locations. That is, according to some embodiments,the area mask 750A can be formed to configure the opening 752A to beother geometric shapes, such as square, circular, a polygon with 3 ormore sides, etc. The initially-formed photo resist mask 753 can beformed completely across the opening in at least one dimension, forexample across the smaller dimension, e.g., in the Y direction from topto bottom of opening 752A as shown in FIG. 7A. The initially-formedphoto resist mask 753 can be formed to overlap the area mask 750A by atleast an amount by which the photo resist mask is reduced in forming astair step times the quantity of stair steps to be formed. That is, theinitially-formed photo resist mask 753 can be formed to overlap the areamask at the top and bottom edges of opening 752A shown in FIG. 7A by anamount equal to the distance between position 757 and 753.

Subsequently, the initially-formed photo resist mask 753 can bere-sized, e.g. formed, to a smaller size and located at the positionshown at dotted outline 754 for a second material removal process,re-sized to a smaller size and located at the position shown at dottedoutline 755 for a third material removal process, re-sized to a smallersize and located at the position shown at dotted outline 756 for afourth material removal process, and re-sized to a smaller size andlocated at the position shown at dotted outline 757 for a fifth materialremoval process. Only one of photo resist masks 753, 754, 755, 756, or757 is formed over the opening 752A at a time. The photo resist masks753, 754, 755, 756, or 757 can be centered over the opening 752A, i.e.,centered in one direction over the opening 752A such that the twoexposed areas 746 are of equal area, as shown in FIG. 7A, or offset fromcenter, as shown in FIG. 7B. The area mask 750A can remain in place, asshown, for all material removal processes. In this manner, a stair stepstructure can be formed within opening 752A, for example, at each sideof opening 752A.

The area mask 750A with opening 752A limits a stair step structure to beformed at only certain portions of a stack of materials, such as at oneedge, two edges, or at only a portion of each of one or two edges, as isdescribed with respect to FIG. 8A-8L. That is, area mask 750A withopening 752A can limit formation of the stair step structure to be atless than all, e.g., four, edges of the stack of materials. The opening752A can be oriented to form one or more stair step structures in the Xdirection, as shown in FIG. 7A, in a Y direction, or in some other,e.g., intermediate, direction. Use of the area mask 750A with opening752A for stair step structure formation can result in narrow width stairstep structures, which allow other signal lines and features to beformed in areas masked by the area mask 750 and/or photo resist mask.The restricted opening 752A, and resulting smaller stair step structure,can result in a smaller overall die size since the area mask can be usedto protect areas where stair step formation is not needed.

FIG. 7B is a block diagram illustrating stair step formation in onedirection using an area mask in accordance with one or more embodimentsof the present disclosure. FIG. 7B shows an area mask 750B having anopening 752B, e.g., window, therethrough formed over the stack ofconductive and insulating materials. A photo resist mask can be formedover the opening 752B as shown at 753, and extending to or past the areamask 750B. According to various embodiments, the photo resist mask canbe formed over a portion of the area of the conductive material exposedthrough opening 752B so as to leave area 746 of the stack, e.g.,conductive material, exposed and subject to material removal. Conductivematerial (and underlying insulating and/or conductive materials) in area748 do not have a portion of the area mask 750B or the photo resistmask, e.g., 753, formed thereover.

As shown in FIG. 7B, a stair step structure can be formed involving area748 at the right side of opening 752B. The photo resist mask can beformed over the area mask 750B with respect to three of four edges ofthe opening 752B, e.g., shaped as a non-square rectangle. The photoresist mask, e.g., 753, is formed such that it covers all of the exposedarea of the conductive material in opening 752B other than one area 748.A first material removal process can be applied to area 748.

Subsequently, the photo resist mask can be re-sized, e.g. formed, asshown at 754 for a second material removal process, re-sized as shown at755 for a third material removal process, re-sized as shown at 756 for afourth material removal process, and re-sized as shown at 757 for afifth material removal process. The area mask 750B can remain in place,as shown, for all material removal processes. In this manner, a stairstep structure can be formed within opening 752B, for example, at theright side of opening 752B.

FIGS. 8A-8L are block diagrams illustrating stair step formation usingan area mask in accordance with one or more embodiments of the presentdisclosure. FIG. 8A shows an end view of a stack 860 of conductivematerials 861. The conductive materials constitute respective stairsteps in the stack 860. The stack 860 can also include insulatingmaterials between the conductive materials 861, which are omitted fromFIGS. 8A-8L for clarity. The quantity, composition and order ofconductive materials to which the method of the present disclosure canbe applied can be the same or different than that shown in this example.For example, the stack 860 can include a plurality of select gateconductive materials, a plurality of access line conductive materials,and/or other conductive and/or insulating materials.

FIG. 8B shows a chop mask material 862, e.g., a hard mask material,formed over stack 860. FIG. 8C shows the chop mask material 862 afterpatterning and etching into area masks 864. FIG. 8D shows the stack 860after further processing to etch the conductive materials 861 (andinsulating materials—not shown) into a number of stack columns 863 basedon the patterning of the area masks 864. FIG. 8E shows the etched stack860 of FIG. 8D after further processing to remove the area masks 864,such as by CMP for example. Although not shown, materials such asinsulating materials, can be deposited into the spaces formed by etchingthe conductive materials 861 (and insulating materials—not shown) basedon the patterning of the area masks 864.

FIG. 8F shows a hard mask material 866 formed over the patterned andetched stack 860. FIG. 8G shows the hard mask material 866 afterpatterning and etching into area mask 868. As shown in FIG. 8G, areamask 868 can extend laterally beyond the edges of the some stack columns863 of conductive material 861. FIG. 8H shows a first 872 and second 870photo resist mask formed over the patterned and etched stack 860 and/orarea mask 868. The first photo resist mask 872 is shown in FIG. 8Hdisposed between portions of area mask 868, and second photo resist mask870 is shown formed over the first photo resist mask 872 and area masks868. Although discrete first 872 and second 870 photo resist masks areshown in FIG. 8H, the photo resist masks can be formed by a single photoresist mask material formation, e.g., deposition.

FIG. 8I shows a top view of the stack 860 after further processing. Cutlines 8J, 8K, and 8L are indicated on FIG. 8I, corresponding to the endviews shown in FIGS. 8J, 8K, and 8L respectively. FIG. 8I shows the areamask 868, e.g., hard mask, after the forming, patterning and etchingdescribed with respect to the previous figures. Area mask 868 has anopening therethrough that configures the area mask to resemble aU-shaped polygon that covers entirely the outermost stack columns 863and partially covers the inner stack columns 863.

A number of photo resist mask configurations can be used in conjunctionwith the area mask 868 to form a stair step structure involving theinner stack columns 863, in the location shown in FIG. 8I. For example,photo resist mask configuration 874, 876, and 878 can be used to patterna stair step structure out of the inner stack columns 863, e.g., theportions of the inner stack columns 863 not removed by first, second,and third material removal processes, as described previously withrespect to previous figures. FIG. 8I shows at least one of the innerstack of columns 863 having a first end, e.g., left end, located in-linewith and adjacent to first ends, e.g., left ends, of the two outerstacks of columns, and at least one inner stack of columns has a secondend, e.g., right end, located not in line with second ends, e.g., rightends, of the two outer stack of columns such that the stair stepstructure is formed at the second end, e.g., right end, of the at leastone inner stack of columns.

FIG. 8J is an end view of the stack 860 taken at cut line 8J shown inFIG. 8I. FIG. 8J reflects the photo resist mask 870 in the third 878photo resist mask configuration, and shows the top conductive materials861 in each of the outer and inner stack columns 863 with the topconductive material remaining as the top step of the stair stepstructure since this portion of the outer and inner stack columns 863 isalways covered by either the area mask 868 or the photo mask 870/872 forall configurations, e.g., 874, 876, 878 of the photo mask 870/872 usedin forming the stair step structure.

FIG. 8K is an end view of the stack 860 taken at cut line 8K shown inFIG. 8I. FIG. 8K also reflects the photo resist mask 870 in the third878 photo resist mask configuration. However, cut line 8K does notintersect photo resist mask 870, which is therefore not shown in FIG.8K. FIG. 8K shows the conductive materials in each of the outer stackcolumns 863 being always covered by the area mask 868 for all materialremoval processes used to form the stair step structure.

FIG. 8K shows the top tier of conductive materials 861 in each of theinner stack columns 863 removed since the inner stack columns 863 at thelocation of cut line 8K are covered by the photo resist mask 870/872 formaterial removal processes involving the first 874 and second 876 photoresist mask configuration, but is not covered for a material removalprocess involving the third 878 photo resist configuration. At thelocation of cut line 8K, the inner stack columns 863 form a middle stepin the stair step structure with the second tier 882 of conductivematerials exposed.

FIG. 8L shows the top two stair steps of conductive materials 861 ineach of the inner stack columns 863 removed since the inner stackcolumns 863 at the location of cut line 8L are covered by the photoresist mask 870/872 for material removal processes involving the first874 photo resist mask configuration, but is not covered for a materialremoval processes involving the second 876 and third 878 photo resistconfigurations. At the location of cut line 8K, the inner stack columns863 form a bottom step in the stair step structure with the third tier880 of conductive materials exposed.

As can be observed in FIG. 8I, the use of the area mask in conjunctionwith a photo resist mask can confine stair step formation to smallerareas and/or to areas closer to other features than can be achieved, forexample, if stair steps are formed around all sides of a photo resistmask used alone, e.g., without an area mask. For instance, stair stepscan be formed on only the inner stack columns 863 as shown in FIG. 8I,where an area mask 868 is used to define, in whole or in part, the areawithin which the stair steps are to be formed using the photo resistmask. In this manner, stair steps can be used in forming coupling fromsmaller and/or more precisely-located areas adjacent a memory array todriver circuitry, for example.

The first material removal can include shortening a length of the atleast one inner stack of columns to be less than a length of the twoouter stacks of columns. Further material removal processes, e.g.,etches, can be used to form the stair step structure at the shortenedend of the at least one inner stack of columns, e.g., the end notaligned with the outer stacks of columns. Although not shown in FIG. 8I,a stair step structure can also be formed in the shortened end of the atleast one inner stack of columns, e.g., the end not aligned with theouter stacks of columns. A stair step structure can also be formed atone or more edges of the outer stacks of columns. That is, an area maskused in conjunction with a photo resist mask can be used to form stairstep structures in a variety of non-uniform shapes and sizes. Theinitial size of the photo resist mask can be sized to overlap the areamask by at least an amount by which it will be removed during etchingand/or trimmed during formation of all, e.g., a plurality, of stairsteps.

As will be appreciated from the foregoing illustrations anddescriptions, an area mask can be used to define areas of the stack atwhich stair step structures are not to be formed. A photo resist maskcan thereafter be used in different footprint configurations, e.g.,shrinking, in areas not protected by the area mask to form one or morestair step structures. The area mask can have an opening therethroughsuch that the area mask is configured to cover some portion of a stackof conductive and/or insulating materials that is not to be etched inany material removal process used to form a stair step structure, andnot cover another portion of the stack of conductive and/or insulatingmaterials that is to be etched in a material removal process used toform a stair step structure. In this manner, stair step formation can beconfined to only those areas in which stair steps are needed in a finalconfiguration of the stack of conductive and/or insulating materials (asopposed to stair step structures being formed and subsequently removed).

Although specific embodiments have been illustrated and describedherein, those of ordinary skill in the art will appreciate that anarrangement calculated to achieve the same results can be substitutedfor the specific embodiments shown. This disclosure is intended to coveradaptations or variations of various embodiments of the presentdisclosure. It is to be understood that the above description has beenmade in an illustrative fashion, and not a restrictive one. Combinationof the above embodiments, and other embodiments not specificallydescribed herein will be apparent to those of skill in the art uponreviewing the above description. The scope of the various embodiments ofthe present disclosure includes other applications in which the abovestructures and methods are used. Therefore, the scope of variousembodiments of the present disclosure should be determined withreference to the appended claims, along with the full range ofequivalents to which such claims are entitled.

In the foregoing Detailed Description, various features are groupedtogether in a single embodiment for the purpose of streamlining thedisclosure. This method of disclosure is not to be interpreted asreflecting an intention that the disclosed embodiments of the presentdisclosure have to use more features than are expressly recited in eachclaim. Rather, as the following claims reflect, inventive subject matterlies in less than all features of a single disclosed embodiment. Thus,the following claims are hereby incorporated into the DetailedDescription, with each claim standing on its own as a separateembodiment.

1-20. (canceled)
 21. An apparatus, comprising: horizontal conductivelines coupled to a string of vertical memory cells, the horizontalconductive lines formed from a stack of alternating conductive materialsand insulating materials having a first stair step structure at a firstedge of the stack and a second stair step structure at a second edge ofthe stack.
 22. The apparatus of claim 21, further comprising a stringdriver coupled to the conductive lines via vertical conductors coupledto respective stair steps of the first stair step structure.
 23. Theapparatus of claim 21, further comprising a string driver coupled to theconductive lines via vertical conductors coupled to respective stairsteps of the second stair step structure.
 24. The apparatus of claim 21,wherein the first stair step structure is at a portion of the first edgeof the stack and a second stair step structure is at a portion of thesecond edge of the stack.
 25. The apparatus of claim 21, wherein thestack of alternating conductive materials and insulating materialsincludes a plurality of stack columns of alternating conductivematerials and insulating materials at the first edge of the stack andthe second edge of the stack, the plurality of stack columns arrangedside-by-side, and wherein a first one of the stack columns at the firstedge of the stack and a first one of the stack columns at the secondedge of the stack has the stair step structure.
 26. The apparatus ofclaim 25, wherein: a second one of the stack columns at the first edgeof the stack is devoid of the stair step structure; and a second one ofthe stack columns at the second edge of the stack is devoid of the stairstep structure.
 27. The apparatus of claim 25, wherein the plurality ofstack columns are arranged side-by-side with inner stack columns beinglocated between outer stack columns, and wherein the inner stack columnshave the stair step structure and the outer stack columns are devoid ofthe stair step structure.
 28. The apparatus of claim 27, the inner stackcolumns have a same first length, and the outer stack columns have asame second length, the first length being shorter than the secondlength.
 29. The apparatus of claim 25, wherein at least one of the firstone of the stack columns at the first edge of the stack and the firstone of the stack columns at the second edge of the stack is of shorterlength than at least one of a second one of the stack columns at thefirst edge of the stack and a second one of the stack columns at thesecond edge of the stack.
 30. The apparatus of claim 25, wherein theplurality of stack columns include at least two outer stack columns thatare devoid of the stair step structure.
 31. An apparatus, comprising: avertical string of memory cells; and horizontal conductive lines coupledto the memory cells, the horizontal conductive lines arranged in a stackof conductive materials separated by insulating materials with aplurality of stack columns of alternating conductive materials andinsulating materials extending from two edges of the stack, some of theplurality of stack columns having a first stair step structure at afirst edge of the stack, and some of the plurality of stack columnshaving a second stair step structure at a second edge of the stack. 32.The apparatus of claim 31, wherein the first stair step structure is atonly a portion of the first edge of the stack and wherein the secondstair step structure is at only a portion of the second edge of thestack.
 33. The apparatus of claim 31, wherein some of the plurality ofstack columns do not have a stair step structure.
 34. The apparatus ofclaim 33, wherein the plurality of stack columns that do not have astair step structure extend further from the stack of conductivematerials than the some of the plurality of stack columns that have astair step structure.
 35. The apparatus of claim 33, wherein: at leasttwo of the plurality of stack columns have a stair step structure andextend from the first edge of the stack between stack columns that donot have a stair step structure; and at least two of the plurality ofstack columns have a stair step structure and extend from the secondedge of the stack between stack columns that do not have a stair stepstructure.
 36. An apparatus, comprising: a vertical string of memorycells; horizontal conductive lines coupled to the memory cells, thehorizontal conductive lines formed from a stack of alternatingconductive materials and insulting materials having a first stair stepstructure at a portion of a first edge of the stack and a second stairstep structure at a portion of a second edge of the stack.
 37. Theapparatus of claim 36, further comprising a string driver coupled to theconductive lines via vertical conductors coupled to: respective stairsteps of the first stair step structure; and respective stair steps ofthe second stair step structure.
 38. The apparatus of claim 37, whereinthe string driver has a substantially planar structure.
 39. Theapparatus of claim 36, wherein the string of memory cells comprises athree dimensional NAND string.
 40. The apparatus of claim 36, whereinthe first stair step structure is formed only at the portion of thefirst edge of the stack, and wherein the second stair step structure isformed only at the portion of the second edge of the stack.